Finite Element stress analyses of normal, arthritic and prosthetic knee joints will be developed to analyze the mechanics of the degenerative process and to optimize prosthetic replacement procedures. Existing 3-dimensional models of the tibio-femoral joint and the patella will be generalized to include ligament forces and the nonuniform distribution of trabecular bone density. New models will be developed for: 1) tibial component fixation in prosthetic knees; 2) patellar resurfacing procedures; and 3) a spherical pore geometry representing the microstructure of trabecular bone and the cement/bone interface. To provide material properties for the finite element models, the spatial variation in the viscoelastic properties of articular cartilage will be measured using a flow-independent method. Previous experiments on the density dependence of trabecular bone will be extended to anisotropic loadings and biaxial stresses. A pure-shear specimen geometry will be used to determine the shear strength of trabecular bone, PMMA and the cement/bone interface. Trabecular bone densities in normal and degenerative cadaver knees will also be determined by computerized tomography and the data input into the finite element models. Estimates on model accuracy will be provided by in vitro studies of excised cadaver knees using reflected light photoelasticity and strain gage rosettes and by 3-dimensional stereologic analyses of the normal patella. The procedures will be used to optimize methods for tibial and patellar component fixation and to explore hypotheses on the mechanics of Wolff's Law, arthritic degeneration and chrondromalacia.